C语言小练习

题目2. 输入一个圆半径r，当r>＝0时，计算并输出圆的面积和周长，否则，输出提示信息。

#include 
   #define PI 3.14 
int main(voi 	d)
{ double  r ,area , girth;  
 printf("please input r:n");
 scanf("%lf",&r);
	 if (r>=0)                        
	      { area =PI*r*r;
           girth =2*PI*r ;
	        printf("the area is %.2fn", area);	
printf("the girth is %.2fn", girth);}
else  
printf("Input error!n"); 
return 0;
 }